Cathode ray tube



Dec. `31, 1940.

K.SCHLESNGER GATHODE RAY TUBE vFiled July 8, 1933 17 E79 11 Fig. 3

Iriver: for:

Wfw

Patented Dec. 31, 1940 UNITED STATES PATENT OFFICE l CATHODE RAY TUBEKurt Schlesinger, Berlin, Germany, assignor, Vby

mesne assignments, to Loewe Radio, Inc., a corporation of New YorkApplication July 8, 1938, Serial No. 218,165 In Germany August 30, 19374 Claims.

of thev cathode is produced between the'cathode` 10i-and the mainreproducing lens. At this point of intersection a diaphragm for thepurpose of obtaining particularly defined conditions is provided. As bythe following electron-optic arrangement the aperture of this diaphragmis pro- 1151 jected upon the screen in somewhat reduced size itsdiameter must not surpass a small multiple of the image point, say-.Bmm.

ri"he object of the invention is a special arrangement of the cathodeand the adjacent electrodes 20 of a cathode ray tube and particularly ofthe said diaphragm to ensure that the intermediate image remainsunaltered inits position in rela tion lto the main reproducing lens,when the rintensity of the cathode ray is controlled.

According to the invention, the opening in the diaphragm is preferablymade to be .3.5mm. in diameter.

The invention may be more clearly understood by reference to theaccompanying drawing. Figs. 30 1-3 showin a purely diagrammatic fashionand by way of example various kinds of electronop` tical systems to beused in a tube according to the invention. In the drawing longitudinalsections through the tubes are shown.`

35' Fig. 1 shows a tube having a cathode I, the

emissive surface of which has a concave shape, a

diameter of approximately 2 mm. and a radius of curvature ofapproximately l-1.5 mm., a control grid situated in front of the same,the open- 40; ing in which grid has a smaller diameter than the hollowcathode, and a first suctional anode 3, which follows on the grid andthe diameter of the opening of which, in turn. is smaller than that ofthe grid. The point of `intersection oc- 4,5` curring in the path of therays at thas a diameter amounting to approximately .3 mm. It issurrounded by the diaphragm 4. The diaphragm 4' is raised to thepotential of the first anode 3. It is possible by adjusting the radius50 of curvature of the cathode, or in the case of a given radius ofcurvature by adjusting the potential of the anode 3 and by simultaneousreadjustment of the bias of the grid to remove any variation in size ofthe .image spot on the screen. In

55 the case of the stated diameters of the apertures (Cl. Z50-162) andthe distances apart as shown in the drawing the critical potential ofthe suctional anode 3 was approximately 200 volts. The grid biasamounted to between 4.0 and l volts and the slope on an average to 3 mA.over 100 volts.

The point of intersection at 4 is reproduced sharply and Without loss onthe screen by a main lens 6. A metallic tube 5 separates the lens zonefrom the preliminary optical system. The perforated plate l acts as mainanode. A rst electron-optical system comprising a diaphragm 8 raised tolow potential and a cylindrical electrode 9 has proved to be very usefulfor obtaining abright image spot devoid of halo effect. In theembodiment shown the tube cover 8 is connected in direct fashion withthe suctional anode 3.

` The ring 9 is very important for holding back interfering secondaryelectrons which are always produced at the diaphragm 8. ing connected indirect fashion with the cathode I.

In the arrangement according to Fig. 2 the bias at the rst anode 3 isconsiderably` greater than in that according to Fig. 1. The cathode I isdesigned as a iiat cathode. Owing to the high potential at 3 it isaccomplished that the system 2/3 does not exert any refractive effect,so that the direction of the single cathode rays remains un-affected bythe grid potential. The possibility of makingthe cathode surface largerthan the area of the aperture in 2 results in the considerable advantagethat centering errors of the cathode member have not the least effect.Behind the first anode 3 there is located a lrst lens comprising acylinder I2, which is connected for example with the cathode, and thediaphragm 8. The electrode 8 is connectedin direct fashion to thetubular member 5. If the lens cylinder I2 has approximately the samepotential as the cathode I, a cross-over point is formed at 4. At thispoint there is included in the path of the rays the stated perforateddiaphragm 4. As regards potential, this diaphragm is raised to thepotential of the first anode 3. In order to avoid secondary emission thediaphragm may consist, at least on its surface, of a substance, such asgraphite or hard carbon, which is incapable of performing secondaryemission. With an effective cathode surface having a diameter of 1.5 mm.there is obtained with a spacing between and 4 amounting to 10 mm. adiameter of the intersection point of such kind that the same can .beenclosed practically without loss by a diaphragm having a diameter of.3-.5 mm.

The reproducing lens following thereon may It is shown as be' "-1,"correspond to that set forth in Fig. 1. On occasion it has been foundconvenient, for the purpose of elminiating the halo of the image pointcaused by secondary emission at the diaphragm 4, to provide a specialguard ring of approximately 5 mm. in diameter behind the diaphragm, thisring being connected with a very negative potential,l for example withthe potential of the cathode. This ring exerts a returning action on thesecondary rays deviating at a Very large angle from the axis of thebeam, and leaves the main rays unaffected.

A further possible embodiment of the invention is illustrated in Fig.3.` The cathode I is again a hollow cathode and forms'together with thecontrol grid 2 and the anode 3 the control system. There follow acylindrical ring 9 and a wide-aperture diaphragm 8. The cylinderSreflects the stray electrons. The diaphragm 8 together with the tubularmember 5, which is raised to a higher potential, build up, in themanneralready indicated in the above, a rst electron lens. Themain lens of thetube is constituted A by the upper edge of the tubular member 5 andelement 5a in conjunction with the anode diaphragm 1. v Y Y It has beenfound that it is possible to obtain on the screen a constant diameter ofthe image point, when. the radius of curvature of the emissive surfaceof the cathode is equal to approximately the distance of the centre ofthe cathode from the anode 3. Then all rays from the largesurfacecathode converge to a point of intersection 4.

An arrangement o f this kind is described in the copending U. S. patentapplicationiSer. No. 212,316, filed June 7, 1938.

The cross-over 4 produced by means of Aelements I, 2, 3, is again usedas the object of the electron-optical reproduction on the screen and is,according to the present invention, enclosed by the diaphragm 4. Thelens 5a/I reproduces this point of intersection on the screen 20.

Special means are provided for eliminating the loss of contrast due to ageneral illumination of the screen initially occurring upon` thisreproduction. For this purpose there is provided the above mentionedfirst lens arranged in close proximity to the point of intersection. Theequif potential surfaces indicated in broken lines re-` sult upon thereciprocal of the field of the tubular member 5.

Special means are provided for eliminating the loss of contrast due to ageneral illumination of.

' the screen initially occurring upon this V'reproduction. For thispurpose there is provided the above mentioned first lens. Theequi-potential surfaces indicated in broken lines result upon'thereciprocal of the eld of the tubular member 5, which is raised toapproximately one-third of the anode potential, by reason of theintermediate diaphragm 8, which by means of apotentiometer 24 isadjusted to a lower potential than the tubular member. If the bias ofthe intermediate diaphragm 8 is suitably adjusted at I4, a refractiveplane is built up between the point of intersection and 8.

The diaphragm 8 and 3 can also be provided in fixed connection, and thebias of 5 adjusted alone, from the exterior, at a potentiometer 2l.- Forthis purpose 5 and 5a are separated, as the potential at 5a has alreadybeen pre-determined by adjustment of the sharpness of the image point onthe screen.

I claim :i

1. In a cathode ray tube comprising a target element, an indirectlyheated large surface cathode, a first anode diaphragm, and a controlelectrode having the shape of a diaphragm and being arranged betweensaid cathode and said first anode diaphragm: a cross-over formingelectron optical system including said cathode, said control diaphragm,said rst anode diaphragm and a further diaphragm arranged adjacent tosaid rst anode diaphragm on its side facing said screen and closelysurrounding said cross-over,

the spacing between said first anode diaphragm and said furtherdiaphragm being approximately equal to the spacing between said rstanode diaphragm and said control diaphragm; an electron-optical lenssystem for producing an image of said cross-over on said target element;and means for deflecting said cathode ray to scan said target element.

2. In a cathode ray tube comprising a target element, an indirectlyheated large surface cathode, a first anode diaphragm, and a controlelectrode having the shape of a diaphragm and being arranged betweensaid cathode and said rst anode diaphragm: a cross-over forming electronoptical system including said cathode, Said control diaphragm, vsaid rstanode diaphragm and a further'diaphragm arranged adjacent to said firstanode diaphragm on its side facing said screen and closelyv surroundingsaid cross-over, the spacing between said first anode diaphragm and saidfurther diaphragm being approximately equal to the spacing between saidfirst anode diaphragm and said control diaphragm; an electronopticallens system comprising a cylindrical electrode and a second anodediaphragm for producing an image of said cross-over on said targetelement, said cylindrical electrode and said second anode diaphragmbeing mounted in axial consecution adjacent to said further diaphragm onits side facing said target element, said cylindrical electrode beingelectrically insulated within the tube from said further diaphragm andfrom said second anode'diaphragm; and means for deflecting said cathoderay to scan said target element.

3. In a cathode ray tube comprising a target element, an indirectlyheated large surface cathode, a first anode diaphragm, and a controlelectrode having the shape of a diaphragm and being arranged betweensaid cathode and said rst anode diaphragm: a rst electron-optical systemincluding said cathode, said control diaphragm and said rst anode andadapted to parallel the cathode ray after emergence from said cathode; across-over forming electron-optical system mounted adjacent to saidfirst anode on its side facing said target element and including, inaxial consecution, a cylindrical electrode, a second anode diaphragm,and a further diaphragm closely surrounding said cross-over, saidcylin-` drical electrode being electrically insulated within the tubefrom said first anode diaphragm and from said second anode diaphragm; afurther electron-optical system for producing an image of saidcross-over on said target element; and means for deflecting said cathoderay to scan said target element.

4. In a cathode ray tube comprising a target element, an indirectly,heated large surface cathode, a first anode diaphragm, and a controlelectrode having the shape of a diaphragm and being arranged betweensaid cathode and said nrst anode diaphragm; a rst electron-opticalsystem including said cathode, said control diaphragm and said firstanode and adopted to parallel the cathode rayV after emergence from saidcathode; a cross-over forming electron-optical system mounted adjacentto said first anode on its side facing said screen and including, inaxial consecution, a cylindrical electrode, a second anode diaphragm,and a further diaphragm closely surrounding said cross-over, saidcylindrical electrode being electrically insulated Within the tube fromsaid first anode diaphragm and from said second anodediaphragm, saidfurther diaphragm being connected to said first anode; a furtherelectron-optical system for producing an image of said cross-over onsaid target element; and means for deflecting said cathode ray to scansaid target element.

KURT SCI-ILESINGER.

